The term “transfection” is used herein to denote the introduction of a nucleic acid into a cell. The nucleic acid may be of any origin, and the recipient cell may be prokaryotic or eukaryotic.
Gene therapy and gene vaccination are techniques that offer interesting possibilities for the treatment and/or prophylaxis of a variety of conditions, as does anti-sense therapy. Such techniques require the introduction of a DNA of interest into target cells. The ability to transfer sufficient DNA to specific target cells remains one of the main limitations to the development of gene therapy, anti-sense therapy and gene vaccination. Both viral and non-viral DNA delivery systems have been proposed. In some cases RNA is used instead of DNA.
Receptor-mediated gene delivery is a non-viral method of gene transfer that exploits the physiological cellular process, receptor-mediated endocytosis to internalise DNA. Examples include vectors targeted against insulin receptors, see for example, Rosenkranz et al Experimental Cell Research 199, 323-329 (1992), asialoglycoprotein receptors, see for example, Wu & Wu, Journal of Biological Chemistry 262, 4429-4432 (1987), Chowdhury et al Journal of Biological Chemistry 268, 11265-11271 (1993), and transferrin receptors, see for example, Ciriel et al, Proc. Natl. Acad. Sci. USA 88, 8850-8854 (1991). Further examples of vectors include monoclonal antibodies targeting receptors on neuroblastoma cells (Yano et al, 2000), folate conjugated to liposomes (Reddy & Low 2000, Reddy et al. 1999), galactose for targeting liver cells (Han et al. 1999 Bettinger et al. 1999) and asialogylcoprotein, also for liver cells (Wu et al. 1991).
Receptor-mediated non-viral vectors have several advantages over viral vectors. In particular, they lack pathogenicity; they allow targeted gene delivery to specific cell types and they are not restricted in the size of nucleic acid molecules that can be packaged. Gene expression is achieved only if the nucleic acid component of the complex is released intact from the endosome to the cytoplasm and then crosses the nuclear membrane to access the nuclear transcription machinery. However, transfection efficiency is generally poor relative to viral vectors owing to endosomal degradation of the nucleic acid component, failure of the nucleic acid to enter the nucleus and the exclusion of aggregates larger than about 150 nm from clathrin coated vesicles.
Desirable properties of targeting ligands for vectors are that they should bind to cell-surface receptors with high affinity and specificity and mediate efficient vector internalisation. Short peptides have particular advantages as targeting ligands since they are straightforward to synthesise in high purity and, importantly for in vivo use, they have low immunogenic potential.
WO 98/54347 discloses a mixture comprising an integrin-binding component, a polycationic nucleic acid-binding component, and a lipid component, and also discloses a complex comprising
(i) a nucleic acid, especially a nucleic acid encoding a sequence of interest,
(ii) an integrin-binding component,
(iii) a polycationic nucleic acid-binding component, and
(iv) a lipid component.
The complex is primarily an integrin-mediated transfection vector.
Integrins are a super-family of heterodimeric membrane proteins consisting of several different α and β subunits. They are important for attachment of cells to the extracellular matrix, cell-cell interactions and signal transduction.
Integrin-mediated internalisation proceeds by a phagocytic-like process allowing the internalisation of bacterial cells one to two micrometers in diameter (Isberg, 1991). Targeting of non-viral vectors to integrins, therefore, has the potential to transfect cells in a process that mimics infection of cells by pathogens and avoids the size limitation imposed by clathrin-coated vesicles in receptor-mediated endocytosis.
It is considered that the components described in WO 98/54347 associate electrostatically to form the vector complex, the vector being of the lipopolyplex type. The vector complexes of WO 98/54347 are found to transfect a range of cell lines and primary cell cultures with high efficiency, with integrin specificity and with low toxicity. For example, vascular smooth muscle cells are transfected with 50% efficiency, endothelial cells with 30% efficiency and haematopoietic cells with 10% efficiency. Furthermore, in vivo transfection of bronchial epithelium of rat lung and pig lung with an efficiency comparable with that of an adenoviral vector has been demonstrated.
Vectors that utilise integrin receptors to mediate gene transfer have the advantage that they target a large number of different types of cells in the body as integrin receptors are relatively widespread. In some circumstances, for example, in in vivo treatment, however, it may be preferable to target recipient cells more specifically.